This invention relates to a hydraulic brake system for automotive vehicles with a master brake cylinder and with a power booster connected upstream of the master brake cylinder, in which a pressure medium pump which may be driven by an electric motor is used for providing an auxiliary hydraulic energy, the drive of which may be switched on by a pressure accumulator, on the one hand, and by a brake pedal contact, on the other hand, in the unbraked operation of the automotive vehicle the pressure accumulator permanently being kept on a pressure level sufficient for an initial actuation of the brake and the charge of the pressure accumulator being monitored by a pressure control valve.
A hydraulic brake system featuring the above characteristics is described in the prior patent application No. P 32 47 498.9. In the hydraulic brake system according to the prior suggestion the delivery side of the pressure medium pump is communicating with the inlet of a pressure medium accumulator via a pressure control valve. Thus during the operation of the automotive vehicle there will be always a predeterminable fluid volume available in the pressure accumulator. To this end, the pressure accumulator disposes over an electric contact which is operable in dependence on the charge of the pressure accumulator and which is connected with the electric motor drive of the pressure medium pump.
In the hydraulic brake system according to the prior suggestion the pressure control valve consequently only serves to monitor the accumulator charge of the hydropneumatic pressure accumulator. As soon as an actuating force is exerted on the brake pedal and the power booster connected upstream of the master brake cylinder adopts an operating position, the fluid volume available in the pressure accumulator will be supplied to the hydraulic power booster. Thus there will be an auxiliary force assistance as early as in the initial phase of the braking action although there is no need for the pressure medium pump to operate in the initial phase of braking.
Due to the relatively small accumulator volume of the hydropneumatic pressure accumulator the pressure fluid volume that has accumulated in the pressure accumulator will be depleted relatively fast. Thus an electric contact at the pressure accumulator will be closed which will switch on the electric motor drive of the pressure medium pump. Thus, upon a continued braking action, the delivery side of the pressure medium pump will permanently communicate with the hydraulic power booster. Thus the delivery provided by the pressure medium pump will be available as auxiliary energy at the hydraulic power booster.
In the described brake system it is to be considered less advantageous that the pressure medium pump whose drive, upon the brake's actuation, remains switched on permanently due to a respective brake pedal contact also wants to charge the pressure accumulator of the hydraulic brake system. Thus, at least partially, the delivery provided by the pressure medium pump will be led into two channels connected in parallel, the hydraulic power booster of the brake system, of course, not being provided with the maximum delivery of the pressure medium pump. Even upon an actuation of the brake, rather, there will be a recharging of the pressure medium accumulator after the pressure medium accumulator had been discharged. Thus, possibly the delivery pressure of the pressure medium pump which will be required at the hydraulic power booster at least temporarily will not be available.
It is thus an object of the present invention to further develop a hydraulic brake system of the type referred to above so as to prevent a new recharging of the pressure medium accumulator after the depletion of said pressure medium accumulator upon the actuation of the brake, thus the entire auxiliary energy made available by the pressure medium pump directly reaching the hydraulic brake booster.